[Bug 1931035] [NEW] Firefox broken on second monitor

[BillCarlson]

Public bug reported:

After update to firefox 89.0+build2-0ubuntu0.18.04.2, firefox appeared
completely broken. Restored history showed a bunch of blank or messed up
windows (NOT pages). My system is dual monitor with one monitor in
portrait mode.

As part of chasing a fix in a clean profile, got lucky and moved a
window to the main, landscape monitor and lo`, it drew correctly. Moving
window half on one monitor, half on second showed a working half and
messed up half.

Starting Firefox in safe-mode on second monitor worked correctly. Only
extension in place is uBlock Origin. See screenshot.

System is Bionic 18.04 updated 2021-06-05, after which issue noted.

Please advise if additional information is needed.

** Affects: firefox (Ubuntu)
     Importance: Undecided
         Status: New


** Tags: firefox

** Attachment added: "Screenshot showing issue"
   https://bugs.launchpad.net/bugs/1931035/+attachment/5502843/+files/Screenshot_2021-06-06_13-32-00.png

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Title:
  Firefox broken on second monitor

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